1. Field of the Invention
This invention relates to impeller pumps, and particularly to impeller pumps for use as the primary pumps by which a liquid metal, such as sodium, is circulated as the primary coolant in a fast nuclear reactor.
2. Description of Related Art
In such a reactor the liquid metal circulates from the pumps, of which there are several, through the reactor core for the cooling thereof, and then through heat exchangers for transfer of heat to a secondary coolant before return to the suction side of the pumps.
In the interest of economy there is an incentive to increase the rotational speed of the primary pumps, in order to reduce the overall pump size and to enable fewer individual pumps to achieve a given duty. However, a limit is imposed on the increase in rotational speed by the onset of cavitation which can give rise to rapid wear of the impeller, especially when the nature of the circulation is such that vapour bubbles implode at the impeller surfaces, leading to erosion and pitting.